1. Field of the Invention
This invention relates, in general, to copying apparatus and methods and more specifically, to apparatus and methods which scan documents and convert the scanned signals into binary data for printing to form reproductions.
2. Description Relative to the Prior Art
In the electronic copying arts, an original image, such as on a document, is sampled periodically to produce a digital representation of the original image. The digital image is processed by applying image processing functions to improve such image qualities as sharpness and tone-scale. The processed digital image is then reproduced on an output medium such as photographic film or paper, a thermal-sensitive medium or otherwise reproduced on plain paper using an ink jet or an electrostatic printer. Examples of the latter may be electrophotographic printers which use laser or light-emitting diodes to form images on a photoconductive medium which is then toned and the toned images transferred to plain paper or a transparency. Typically, the image might be scanned at one resolution, say 400 dots per inch (d.p.i) and printed at a different resolution, say 300 d.p.i.
Where the input scanning resolution is not matched with the output printing resolution, the resolution conversion of data is necessary. Various resolution conversion methods are known in the prior art. However, the devices known in the prior art generally do not provide decimated images with good rendition because the decimation process does not take into account the type of data being decimated. For example, blocks of data representing thin or thick lines may not be distinguished during the decimation process.
It is therefore an object of the invention to provide an improved method and apparatus for decimation, i.e., compression, of binary data to match the decimated data with the resolution of the printer and which is adapted to provide enhanced rendition of line structure.